A safe drinking water supply is a fundamental requirement worldwide. However, more than one billion people lack an adequate supply of safe drinking water. In developing countries and in very rural or remote areas, the critical need is for a drinking water supply free of contamination which can cause acute and potentially fatal illnesses such as bacterial, parasitic and viral diseases. The World Bank estimated in 1992 that more than two million children under five years of age die of diarrhea each year because they do not have access to clean water. Therefore, the goal in these areas is to provide drinking water which meets World Health Organization (WHO) guidelines for "turbidity" and "microbiological and biological content."
Turbidity refers to the cloudiness or muddiness of water, and is defined in the "Standard Methods for the Examination of Water and Wastewater," 18th Edition, American Public Health Association, edited by Greenberg, et al. (1992), as ". . . an expression of the optical property that causes light to be scattered and absorbed rather than transmitted in straight lines through the water! sample." Turbidity, expressed in Nephelometric Turbidity Units (NTU), is determined with a nephelometric turbidimeter, an instrument which compares the intensity of light scattered by water under defined conditions with the intensity of light scattered by a standard reference suspension under the same conditions. The higher the intensity of scattered light, the higher the turbidity. Microbiological and biological (microbiological/biological) content refers to the level of pathogenic organisms in water, and is normally measured by looking for the presence of indicator or surrogate organisms whose presence indicates the probable presence of pathogenic organisms. The coliform group of bacteria is used as the principal indicator of water quality because the coliform group density is typically much greater in water as compared with other organisms. Examples of other pathogenic organisms found in water include enteric viruses as well as macroorganisms such as Giardia lamblia, Entamoeba histolytica, and Cryptosporidium parvum. Elimination of possible harmful chemical contamination is not yet a priority in most of these areas since the life expectancy is generally less than the average time necessary to develop chronic illnesses such as cancer.
Safe drinking water is also a critical need worldwide after natural catastrophes and during armed conflicts. The ability to maintain an adequate supply of safe drinking water can also be difficult for certain industries such as mining or road building, or remote institutions such as field hospitals and clinics. Furthermore, the need for a "point-of-use" drinking water supply is also applicable in U.S. national parks and forests, or other locations which serve a transient population. In the United States, however, drinking water must also meet the standards of the Safe Water Drinking Act.
Drinking water which has low turbidity and microbiological/biological content can be produced from ground or surface fresh water supplies by various methods. A typical water treatment system involves rapid rate filtration through sand media. This method can produce as much as about 300-350 cubic meters of water per day per square meter (m.sup.3 /day/m.sup.2). However, since the particulates removed by the filters penetrate deep into the filter bed, the filter bed needs to be cleaned at regular intervals to prevent plugging. Furthermore, most suspended solids (dirt and microorganisms) are negatively-charged because there is an excess of negative ions on the surface of the particles themselves. Therefore, this method of rapid rate filtration requires chemical pretreatment of the raw water with a coagulant such as alum (hydrated aluminum sulfate) or an organic polymer to impart a positive charge to the negatively-charged solids. In this way, an electrostatic attractive force is created between the suspended solids and the negatively-charged filtration media, so that the filter media can effectively filter out the suspended solids. Other pretreatment steps typically include flocculation and sedimentation following the chemical addition. Flocculation is necessary to mix the suspended solids and coagulants together to produce a precipitate or floc that becomes large enough to settle. Sedimentation allows the floc to settle to the bottom of a tank while the clearer supernate containing the residual positively-charged suspended solids is removed at the top for subsequent passage through the filter media. Although treatment plants can produce quality water with this method, the required capital, labor and resources required to build and operate such a system makes it virtually unavailable in many parts of the world.
A process for the removal of metal ions from water which comprises filtering the water through a bed or layer of granular lightburned or hardburned magnesium oxide is disclosed in U.S. Pat. No. 5,211,852 to Van de Walle, et al. This process is not directed to removing particulates or producing potable drinking water, but to reducing toxic metal ion pollutants which are released by industry into the waterways.
U.S. Pat. No. 4,385,998 to Schiller, et al., discloses the use of magnesium oxide (MgO) for filtering suspended solids from water sources such as process effluents, but does not disclose a method or apparatus for a community drinking water purification system.
Thus, what is needed is a technically simple, cost-effective, and reliable method for producing potable drinking water from ground and surface fresh water supplies during emergencies worldwide, and at all times in developing countries and rural or remote areas.